Metal nanowires (NWs) hold promise for commercial applications such as flexible displays, solar cells, catalysts and heat dissipaters. Among many synthesis approaches, polyol methods are the most widely used methods to produce metal NWs in large quantities with promising potential to meet the scale-up challenges for industrialization needs.
However, polyol methods not only yield nanowires but also other low-aspect ratio shapes (e. g. nanoparticles (NPs) and nanorods (NRs)). Inevitably, these by-products are almost always produced due to the non-instantaneous nucleation and the diffusion-limited crystal growth, which causes the particles to grow along multiple pathways. Moreover, with increasing synthetic scales (e.g. volume) that yield more inhomogeneous conditions, nanoparticles with unpredictable shapes may occupy even higher percentage of the products.
The presence of these undesired NP side-products reduces the NW purity, and can degrade the performance of nanowire-enabled applications and devices. For example, metal nanowire-based transparent electrodes benefit from the optical transparency of a percolated nanowire thin film, yet the NP impurities do not contribute to electrical conductivity while serve as deleterious light scattering centers to reduce light transmission.
Copper nanowires (Cu NWs) are one-dimensional copper nanocrystals that have become desirable for flexible conductive ink in extrusion-based additive manufacturing, for example, direct ink writing. Furthermore, the highly desirable conductivity property of Cu NWs also benefit such applications as transparent electrodes, aerogels, and catalysts for liquid fuel generation, heat dissipaters, etc.
Copper NWs (Cu NWs) may be synthesized using different methods, for example, polyol solution-based synthesis, template-assisted synthesis, electrolyzed deposition, and hydrothermal synthesis, vapor-to-solid synthesis, etc. The preferable polyol method uses a surfactant as a capping agent and is carried out in an aqueous solution at low-temperatures and under ambient conditions that are particularly suitable for large-scale production with low cost.
Following synthesis by some methods, Cu NWs inevitably are accompanied by large quantities of Cu nanoparticles (Cu NPs) as side products. In some applications, the Cu NPs may be undesirable as they may be deleterious for device performance. However, in other applications, the purification of Cu NPs may be preferable to the Cu NWs. Thus, isolation and purification of each population would be advantageous.
NWs and NPs are difficult to separate after synthesis because they are synthesized in the same pot and have similar physical and chemical properties. Methods to separate NPs from NWs have been laborious, expensive, and require bulky centrifugation set-up. Thus, these methods are difficult to scale up. In addition, these methods do not produce high-purity NWs or NPs.
Accordingly, it would be desirable to efficiently separate and purify nanowires and nanoparticles with 100% separation yield. In the case of copper nanowires, it would be desirable to isolate highly purified copper nanowires.